Drop-Downs of an Outer Rotor Flywheel in Different Planetary Touch-Down Bearing Designs

Benedikt Schüßler,Timo Hopf,Stephan Rinderknecht

doi:10.3390/act11020030

Abstract

With an increase in renewable energy in the electricity grid, more storage capacity for grid stabilization and energy flexibilization is necessary. Dynamic grid stabilization is one possible application for flywheels. To increase the energy density of flywheels, they can be built as highly integrated outer rotor systems. The losses of the flywheel are reduced by magnetic levitation and operation under vacuum conditions. In the case of the failure or overload of the active magnetic bearings, the system needs touch-down bearings to prevent system destruction. Planetary touch-down bearings consisting of several small bearing units circumferentially distributed around the stator are especially suited for these systems. In the literature, these planetary touch-down bearings are rarely investigated, especially the number of bearing units. Therefore, this paper investigates the influence of the number of touch-down bearing elements in simulations and experiments for an 8-element and a 6-element touch-down bearing arrangement. For the investigation, drop-downs at four different speeds were performed. Simulation and experimental results showed that, for the 6-element touch-down bearing, in contrast to the 8-element touch-down bearing, maximal velocity did not increase with the drop-down speed. Therefore, the touch-down bearing arrangement with fewer elements is preferrable.

Highlights

With an increase in renewable energy in the grid, more storage systems for grid stabilization and energy flexibilization are needed
Two different planetary touch-down bearings (TDB) designs for outer rotor flywheels were investigated in simulations and experiments on the SWIVT290 prototype
The results of the simulations showed that, for the 6-element TDB, the maximal force during the drop-downs was nearly independent of the drop-down frequency

Summary

Introduction

With an increase in renewable energy in the grid, more storage systems for grid stabilization and energy flexibilization are needed. Planetary TDB consist of several small bearing units that are circumferentially distributed around the stator. This TDB design has certain advantages compared to a conventional TDB consisting of one rolling element bearing. Whirling is more likely to occur for vertical rotors than for horizontal ones because the gravity force in horizontal systems has a whirlsuppressing effect, which was shown in the literature for a planetary design with pins instead of rolling element bearings [5,6]. The planetary TDB design applied in the flywheel showed its capabilities to withstand multiple high speed drop-downs in an vertical inner rotor test rig [7,8]. This paper investigates the system behavior under complete

Methods

Results

Conclusion